Torsional fixing device, especially for the housing of a measuring transducer

ABSTRACT

For limiting twist of a measurement transmitter housing relative to a sensor element, onto which the measurement transmitter housing is screwed, axial barriers are provided, so that the axial position of the measurement transmitter housing relative to the sensor element is limited to a range between two extreme positions defined by the axial barriers. The axial barriers are preferably formed by a ring, which engages both an annular groove in an outer, lateral surface of the sensor element and an annular groove in a cylindrical duct of the transmitter housing.

The present invention concerns twist limiting features, such as can beused, for example, for housings of electrical devices, for examplemeasurement transmitters.

Such housings are frequently embodied in two parts, with a first part ofthe housing being twistable with respect to a second part through apredetermined angular range, in order to rotate, for example, display oroperating elements, which are arranged on the first housing part, into adesired orientation. Since cable frequently extends between the firstand second housing parts, the angular range must be limited, in order toprevent a damaging of the cable or components connected therewith.

Differential pressure transmitters of the assignee, available under thename “Deltabar”, exhibit a twist limiting feature which may be describedas follows. The first housing part has a tubular, first connectingflange with an internal thread, which is screwed onto an external threadof a complementary, second connecting flange of the second housing part.From the cylindrical, outer lateral surface of the second connectingflange, a stop lug extends radially outwards, in a section which isaxially separated from the first connecting flange. Following thescrewing of the first connecting flange onto the second connectingflange, a metal tongue is mounted on the outer, lateral surface of thefirst connecting flange. The metal tongue extends in the axial directionacross the first connecting flange and beyond, and overlaps the stop lugin the axial direction. Twist of the second connecting flange withrespect to the first connecting flange is, as a result, limited in bothdirections by the hitting of the metal tongue on the stop lug. Althoughthis described, twist limiting feature is reliable, nevertheless itsmanufacture and mounting are involved.

The described problem concerns not only pressure sensors, but, quitegenerally, all sensors of the technology of industrial processmeasurements, especially flow rate sensors, viscosity sensors, filllevel sensors, pH-sensors and other potentiometric sensors, temperaturesensors, moisture and humidity sensors, gas sensors and turbiditysensors.

An object of the present invention, therefore, is to provide a devicehaving a twist limiting feature for parts of the device which screwtogether, especially housing parts.

The object is achieved according to the invention by the device of theindependent claim 1.

The device of the invention includes a housing element, which has afirst thread; and a second element, which has a second threadcomplementary to the first thread and engaged therewith. The housingelement and the second element are twistable with respect to one anotherabout the axis of the two threads, and the twist results in a change oftheir relative axial positions, due to the pitch of the threads. Thedevice additionally exhibits a twist limiting feature, which limits thetwisting of the housing element relative to the second element to anangular range. The twist limiting feature includes two axial barriers,whereby the axial position of the housing element relative to the secondelement is limited to a range between two extreme positions defined bythe axial barriers.

Preferably, the axial barriers are so arranged that the differencebetween the extreme positions corresponds to the axial shift caused by atwisting of the housing element by the maximum allowable angle of twistrelative to the second element, at the given pitch of the thread.

An axial barrier preferably includes, on at least one of the elements,i.e. the housing element or the second element, a preferablyrotationally symmetric, axial stop surface, which serves as a barrierfor a stop, respectively coupling, member coupled with the, in eachcase, other element in such a way that the freedom of movement of thestop member is limited relative to the other element, at least in theaxial direction. The limiting of the freedom of movement can likewise beassured by axial stop surfaces on the other element, or the stop membercan be connected fixedly with the other element.

Axial stop surfaces can be formed especially by radial steps between twocoaxial, cylindrical sections. For this purpose, a lateral surface ofthe housing element, respectively a lateral surface of the secondelement, can have such cylindrical sections. Especially, the lateralsurface of a cylindrical section of the housing element or of the secondelement can have an annularly running groove, which extends radiallyinwards and is limited in the axial direction by first and second radialsteps, with the first and the second radial steps each serving as anaxial stop surface for one of the two axial barriers.

Likewise, the housing element or the second element can include at leastone duct with cylindrical sections of different radii, whose axis ofrotation is aligned with the axis of the threads, with there beingformed between at least two sections of different radii a radial step,which serves as an axial stop surface for an axial barrier of the twistlimiting feature. Especially, there can be provided in the lateralsurface of a cylindrical duct of the housing element or the secondelement an annular groove, which extends radially outwards and isbounded in the axial direction by first and second radial steps, withthe first and second radial steps serving each as an axial stop surfacefor one of the two axial barriers.

To serve as the stop member, a pin or a protrusion can be provided,which is fixedly connected with the, in each case, other element, i.e.the element which does not have the groove, and protrudes radiallyinwards, or radially outwards, as the case may be, into the groove.

Currently especially preferred is a form of embodiment, in which a stopring is engaged with a first, radially outwardly extending groove andwith a second, radially inwardly extending groove, with the first nutbeing located in the lateral surface of a cylindrical duct in thehousing element, or in the second element, as the case may be, and withthe other element having a cylindrical section, in whose lateral surfacethe second groove is located, with the cylindrical section being locatedin the cylindrical duct in such a way that the first groove overlaps atleast partially with second groove in the axial direction.

The stop ring is, in an especially preferred form of embodiment, aspring ring, or an annular washer which is radially flexible.

The stop ring comprises, preferably, a softer material than the materialin which the grooves are formed. For example, the housing element andthe second element can feature, at least sectionally, a metal,especially steel, cast iron, or aluminum, while the stop ring preferablyfeatures a synthetic material, especially an elastomer or athermoplastic material.

In a currently preferred form of embodiment, the screwed connection ofthe housing element with the second element, with interposition of thestop ring, is irreversible to the extent that release of the screwedconnection is not possible without a destruction of the stop ring. Thestop ring can, consequently, also serve the function of a seal, whoseintegrity can, for example, be a prerequisite for performances underguarantee.

The axial dimension of the stop ring, i.e. especially its materialthickness, is preferably so matched to the width of the first and secondgrooves that the sum of the widths of the first and second grooves,minus twice the axial dimension corresponds to the axial shift resultingat the given pitch of the thread from a rotation of the housing elementrelative to the second element by the maximum allowable angle of twist.

The maximum angle of twist should not be more than 720°, thus two fullrotations. In a currently preferred form of embodiment, the maximumangle of twist is 360°. With this, the housing element and the secondelement can assume any orientation with respect to one another. This isespecially of interest for forms of embodiment where the housing elementhas a display field and/or operating elements, which are to be orientedoptimally for the operator.

For applications in process measurement technology, the housing elementcomprises, preferably, a measurement transmitter housing, with thesecond element preferably exhibiting a connection adapter, or a sensorhousing, for connection to the measurement transmitter housing.

The invention will now be explained in greater detail on the basis of anexample of an embodiment illustrated in the drawings, the figures ofwhich show as follows:

FIG. 1 a perspective view of a device of the invention, including ameasurement transmitter and a sensor;

FIG. 2 a detail view of longitudinal sections through the device of theinvention, showing the connection between the measurement transmitterhousing and the sensor housing; and

FIG. 3 a stop ring of a device of the invention.

The measurement transmitter housing 1 shown in FIG. 1 has a drum-shapedhousing section 11, in which usually electronic components, especiallycomponents for data communication, are arranged. In the lateral surfaceof the drum-shaped housing section 11, an duct is provided, which isdefined by an essentially tube-shaped connection flange 10, into whichis screwed a sensor element 2. This sensor element 2 is portrayed inFIG. 1 as a solid block, since the internal structure of the sensorelement 2 is not of concern for the present invention. The sensorelement 2 exhibits, at least sectionally, a cylindrical transmitterconnection 20, which is screwed into the duct 20 of the tubularconnection flange 10. For this purpose, there is provided on the outerlateral surface of the transmitter connection 20 a threaded section,which engages a complementary internal thread 13 on the inner wall ofthe connection flange 10. The sensor element 2 has additionally in thisexample of an embodiment a cylindrical process connection plug 21, whoselateral surface is provided with a thread, with which the sensor elementcan be secured, for example, to a suitable container or opening in aline. It is apparent for those skilled in the art that suitable sealsare to be provided, but this does not need to be detailed for thepresent invention.

The measurement transmitter 1 has on an end face of the drum-shapedhousing section 11 a display 12. In order to be able to turn thisdisplay into any orientation, the measurement transmitter housing mustbe twistable relative to the sensor element 2. The twistablity is,however, limited to a small, angular range, in order, for example, toavoid damaging cables extending from the sensor element 2 into thetransmitter housing 1. This is assured by the twist limiting feature ofthe invention, which employs two, axial barriers to limit the axialposition of the transmitter housing 1 relative to the sensor element toa range covered due to the pitch of the internal thread 13 when thetransmitter housing 1 is turned about the thread axis by the maximumallowable angle of rotation. Details concerning the twist limitingfeature will now be explained on the basis of FIGS. 2 and 3.

FIG. 2 shows two views of a longitudinal section through the tube-shapedconnection flange 10 of the transmitter housing 1, into which thetransmitter connection 20 of the sensor element 2 has been screwed. Eachview shows transmitter connection 20 in a different axial position.

The tubular connection flange 10 has in its inner wall a first annulargroove 14 extending radially outwards. The first annular groove 14 isbounded by two radial steps, whose axial separation from one anotherdefines the breadth B1 of the first annular groove 14. In similarmanner, the transmitter connector 20 has on its outer lateral surface anannular groove 22, which extends radially inwards. The second annulargroove 22 is likewise bounded by two radial steps, whose axialseparation from one another defines the second breadth B2 of the secondannular groove 22.

The radial steps, which bound the first and second annular grooves,serve as axial stop surfaces for a stop ring 3. The stop ring 3 engagesboth the first annular groove 14 and the second annular groove 22, i.e.the outer radius R_(o) of the stop ring 3 is greater than the radius ofthe inner wall of the connection flange 10 in the section from which thefirst annular groove extends radially outwards, and the inner radiusR_(i) of the stop ring 3 is smaller than the radius of the outer lateralsurface of the connection flange 20 in the section from which the secondannular groove 22 extends radially inwards.

The stop ring 3 has an upper face 30 and a lower face 31, which arepreferably at least sectionally parallel to one another. The faces 30,31 form together with the axial stop surfaces, axial barriers forlimiting the movement of the transmitter housing 1 relative to thesensor element 2. The effect of the axial barriers is described in thefollowing. The concepts “above”, respectively “below”, designate in thisconnection the directions toward, respectively away from, the processconnection.

The portion a) of FIG. 2 shows the situation, in which the transmitterhousing 1 has reached the lower extreme position relative to the sensorelement 2. In this situation, the inner region of the lower face 31 hitsagainst the lower axial stop surface, which borders the second annulargroove 22, and the outer region of the upper face 30 hits against theupper, axial stop surface, which bounds the first annular groove 14.

The portion b) of FIG. 2 shows the situation, in which the transmitterhousing 1 has reached the upper extreme position relative to the sensorelement 2. In this situation, the outer region of the lower face 31 hitsagainst the lower axial stop surface, which bounds the first annulargroove 14, and the inner region of the upper face 30 hits against theupper axial stop surface, which bounds the second annular groove 22.

The stop ring 3 exhibits in the region of the first annular groove afirst axial thickness T1 and in the region of the second annular groovea second axial thickness T2. In the currently preferred form ofembodiment, the first axial thickness T1 is equal to the second axialthickness T2 (T1=T2=T). Fundamentally, these can, however, be differentfrom one another. The first axial thickness T1 and the second axialthickness T2 of the stop ring, as well as the first breadth B1 of thefirst annular groove and the second breadth B2 of the second annulargroove are so related to one another that the following holds:(B1−T1)+(B2−T2)=S(φmax),where S(φmax) is the axial shift of the thread 13, which accompanies atwisting of the transmitter housing 1 by the maximum angle of twistφmax. For T1=T2=T, B1+B2−2T=S(φmax).

The maximum angle of twist φmax is about 360° in a currently preferredform of embodiment. In such case, the transmitter housing 1 can assumeevery possible orientation relative to the sensor element 2, andconnecting cables extending between the sensor element 2 and thetransmitter housing 1 are subjected to, at most, one revolution.

The stop ring 3 shown in FIG. 3 has an inclined surface 34 on the outeredge of its upper face 30. Additionally, the ring is interrupted by aslit 33, for the purpose of facilitating the mounting of the transmitterhousing on the sensor element 2. The stop ring of this form ofembodiment is preferably made of an elastic material. For the mounting,first the elastic stop ring 3 is installed into the second annulargroove 22. Then, the transmitter housing 1 is screwed onto the sensorelement 2, with the stop ring 3 being pressed by the inner wall of theconnection flange 10 completely into the second annular groove 22, untilthe first annular groove 14 overlaps the second annular groovesufficiently that the stop ring 3 can spring back and engage the firstannular groove 14, whereby the twist limiting feature is completed.

The projection 35 shown in FIG. 3 is an optional feature for fixingrotation of the stop ring relative to the transmitter housing 1. Thisfeature is, however, not essential to the invention. In forms ofembodiment containing this feature, a groove in the axial direction isprovided in the inner wall of the connection flange 10, foraccommodating the projection with sufficient axial play.

Another form of embodiment is distinguished from what has been describedabove in that no stop ring and no first groove are provided. Instead ofthese, at least one stop body, for example a stop pin is fixedlyconnected with the connection flange 20 and extends into the secondannular groove. In this case, the difference between the second breadthand the axial dimension of the stop body determines the thread shift inthe case of twist of the transmitter body by the maximum angle.

The stop pin can, for example, be provided in the form of a bolt, whichis screwed into a radial, traversing, threaded bore in the lateralsurface of the connection flange 10, when the threaded bore overlaps thesecond annular groove. Optionally, a clamping screw can be provided,which fixes a preferred orientation of the transmitter housing relativeto the sensor element. A radial, threaded bore for receiving theclamping screw can be provided especially in the form of a coaxial,threaded bore through the stop pin.

1-12. (canceled)
 13. A device, comprising: a housing element with afirst thread; and a second element with a second thread, which iscomplementary to the first thread and is engaged therewith; said housingelement and said second element are twistable relative to one anotherabout the axis of the two threads, the twisting causes a change of theaxial position of one with respect to the other due to the pitch of thethreads, wherein: a twist limiting feature, limits the twistability ofsaid housing element relative to said second element to an angularrange, and said twist limiting feature comprises two axial barriers, sothat the axial position of said housing element relative to said secondelement is limited to a range between two extreme positions determinedby said axial barriers.
 14. The device as claimed in claim 13, wherein:said axial barriers are so arranged, that the difference between theextreme positions corresponds to the axial shift caused, for giventhread pitch, by a twisting of said housing element relative to saidsecond element by the maximum allowable angle of twist.
 15. The deviceas claimed in claim 13, wherein: one of said housing element and, saidsecond element includes at least two cylindrical sections of differingradii, whose axis of rotation is aligned with the axis of the threads,and between the at least two sections of differing radii, a radial stepis formed, which serves as an axial stop surface for an axial barrier ofsaid twist limiting feature.
 16. The device as claimed in claim 15,wherein: one of said housing element and said second element includes acylindrical section, whose lateral surface includes an inwardlyextending annularly running groove, and is bounded in the axialdirection by first and second radial steps, and said first and secondradial steps each serve for one of said two axial barriers.
 17. Thedevice as claimed in claim 13, wherein: one of said housing element andsaid second element includes at least one duct with cylindrical sectionsof differing radii, whose axis of rotation is aligned with the axis ofthe threads, and between the at least two sections of differing radii, aradial step is formed, which serves as an axial stop surface for anaxial barrier of said twist limiting feature.
 18. The device as claimedin claim 16, wherein: one of said housing element and said secondelement includes a cylindrical duct, whose lateral surface exhibits anannularly running groove, which extends radially outwards and is boundedin the axial direction by a first and a second radial step, and saidfirst and second radial steps each serve as an axial stop surface forone of said two axial barriers.
 19. The device as claimed in claim 18,wherein: said twist limiting feature further comprises a couplingelement, which is engaged both with said radially outwardly extendinggroove and with said radially inwardly extending groove.
 20. The deviceas claimed in claim 19, wherein: said coupling element comprises anannular washer.
 21. The device as claimed in claim 20, wherein: saidannular washer is radially flexible.
 22. The device as claimed in claim19, wherein: said radially inwardly extending groove has a first breadthin the axial direction, and said radially outwardly extending groove hasa second breadth in the axial direction, and the axial thickness of saidcoupling element is selected such that the sum of the first breadth andthe second breadth, minus twice the axial thickness, corresponds to theaxial shift caused at the given pitch of the threads by a twisting ofsaid housing element relative to said second element by the maximumallowable twist angle.
 23. The device as claimed in claim 13, wherein:said second element comprises a sensor element.
 24. The device asclaimed in claim 13, wherein: said housing element includes ameasurement transmitter housing, and the sensor element an industrialprocess measurement sensor, especially a pressure sensor, flow ratesensor, viscosity sensor, fill level sensor, pH-sensor or otherpotentiometric sensor, temperature sensor, moisture or humidity sensor,gas sensor or turbidity sensor.